RF Exposure Issues (long)

[dave at egh.com]

	I have just read through the document called "Measurements of 
Environmental Electromagnetic Fields at Amateur Radio Stations".  After
reading it, I have a few questions/comments which I think are pertinent 
to the calculation of RF exposure:

	1. I have read the definitions of "Controlled Environment" and
	   "Uncontrolled Environment" on page 53.  It is my assumption
	   that the "Controlled Environment" may be considered to be
	   the property owned/rented by the amateur operator, with
	   possible exceptions in the case of multi-family properties.
	   I believe that the "transient passage" covers visitors,
	   invited or uninvited.  Does this seem reasonable, especially
	   to any of you who are familiar with legal nuances?
	   
	2. How can we accurately determine the duty cycle?  I saw Brian's
	   (K6STI) initial estimate of 25%.  Let's say we have the worst
	   case for a CW contest.  This should be the times when we are
	   calling CQ without answers.  (When we are making a qso, we can
	   assume 50% listening time by virtue of the fact that the 
	   received exchange on average takes as long as the sent one.)  
	   During a CQ'ing period, we are probably transmitting 6 seconds 
	   and listening 4.  The rest of the calculation rests critically 
	   on what percentage the duty cycle is for transmit time, i.e.,
	   what is the time length of a space versus a 'dit' or 'dah'.
	   Does anybody have any idea of this percentage?  Perhaps those
	   of you who have written logging programs capable of sending
	   CW have already calculated this.

	3. The comment has been made that higher antennas are going to
	   cause less exposure than lower ones.  I guess this will make 
	   those of us owning 100 foot towers feel pretty good.  However,
	   the example stations in the study were measured at various
	   locations, and on page 24 I see that station C had a very high
	   reading near a section of feedline (nearly 3 times as high as
	   those taken in the immediate vincinity of the xcvr).  Now the
	   100 foot towers with their 250 foot coax runs may have a 
	   problem.  No comment was made as to the quality of coax.  
	   (K6NB - Wayne, if you're on this group, do you by any chance 
	   remember the coax type?) Offhand, this seems to indicate a 
	   problem with the coax.  Is it reasonable to assume that this 
	   was perhaps RG-8 or some other type with a shield ratio less
	   than that of RG-213? (the xcvr was running 1000 watts)?  If so, 
	   will RG-213 give a substantial improvement?  Is this problem 
	   perhaps related to the lack of a balun at the antenna, or just 
	   a bad feedline?  Perhaps Brian, Dean N6BV, or someone else who 
	   has written antenna analysis software could give us some input.  
	   (I apologize to whomever I have left off this list - I'm sure 
	   there are more of you out there who have written these fine 
	   software products.  It also appears that more of us may be 
	   purchasing one of these products in the near future.)  

	4. Antenna heights and coax qualities being equal, it would seem 
	   that the E field strength limits in the 3.0-30 Mhz frequencies
	   (1842/f and 828/f) indicate that we need to concern ourselves
	   more with 10 meters than 20 or possibly 40 (for yagis).  Wire
	   antennas tend to be closer to the ground for 40,80,160 meters,
	   so there is an added uncertainty here.  Fortunately the formula
	   allows a higher E field strength due to the lower f value.
  
	Any thoughts on these observations will be appreciated.

73, Dave Clemons K1VUT